Digital data recorders, such as digital video recorders (DVRs) have been known since at least 1992. Standard DVRs permit users to record broadcast information to a storage device for later playback. Typically, DVRs enable time-shifted (trick-play) modes of operation that are similar to functions found on video cassette recorders, with which most users are familiar. For example, DVRs may have functions such as “pause,” “rewind,” “fast-forward,” “skip,” and “slow motion.” One of the first commercially available DVRs was the MediaStream system developed and marketed by Media4, now part of EchoStar Communications Corporation. In April 1996, Media4 introduced the MediaStream receiver, which was a Digital Video Broadcasting-compliant satellite receiver system with integrated DVR functions. The MediaStream system was designed to both record and present programs simultaneously, allowing one program to be both recorded and presented. The MediaStream receiver system demultiplexed a Moving Picture Experts Group (MPEG) transport stream that contained one or more television programs, for example, and filled separate video packetized elementary stream (PES) and audio PES buffers. The data contained in the buffers was written to disk for later playback in either normal or trick-play mode. The MediaStream system did no intelligent parsing of the input to generate an index to aid in trick-play modes of operation, but merely performed a “brute-force” search of data stored on the hard disk when performing those functions.
Many methods and systems have been developed for creating indices by intelligently parsing broadcast input streams and using index information generated during input to later find and play back appropriate frames of data. One of the earliest of these systems is described in two patents assigned to Imedia Corporation, U.S. Pat. Nos. 5,949,948 and 6,304,714, both to Krause et al. These patents disclose a set-top DVR system for simultaneous presentation and recording of compressed digital data. For example, U.S. Pat. No. 5,949,948 discloses a start-code detector for detecting the beginning of video I-frames in an MPEG data stream, an indexing system that correlates I-frames with addresses in memory, and a trick-play system that searches the index information to determine which frames to play back in trick-play operations. Similarly, U.S. Pat. No. 5,614,940, to Cobbley et al., of Intel, discloses a set-top system that can convert broadcast information to a digital format, generate during input various index data relating to the content of the broadcast information, store both the compressed broadcast data and the related index data, and then retrieve the broadcast data for playback (in normal or trick-play mode) based upon the corresponding index information. Similar, front-end, input-side intelligent parsing and index-based searching methods are disclosed in U.S. Pat. No. 5,956,716 to Kenner, et al., U.S. Pat. No. 5,659,539 to Porter, et al., U.S. Pat. No. 6,167,083 to Sporer, et al., and U.S. Pat. No. 5,577,190 to Peters.
A later recording system, developed at TiVo Inc. and described in the specification of U.S. Pat. No. 6,233,389, to Barton, et al., also employed a specific type of intelligent parsing/indexing during input and prior to storage of the broadcast information on a storage device. The system described in that patent employs a special circuit called a “Media Switch” that generates indices and fills separate appropriate buffers with specific data. The disclosed “Media Switch” mediates between the central processing unit (CPU), storage device, and memory and thus off-loads the intensive index-based processing of the input stream from the CPU to a separate device. Also in the Barton, et al., system, a software “source object” converts the data into data streams and fills a buffer that is assigned by a central software “transform object” that is responsible for overall control of buffer assignment. The software “transform object” then writes the data to a hard disk. The software “transform object” is also responsible for reading data from the hard disk, filling buffers with the data, and assigning the filled buffers to a software “sink object” for later decoding and playback.
These earlier systems may be inefficient and overly complicated in some operational settings. Such systems require intensive processing during input of the entire set of broadcast data. Given the high throughput required for modern DVR functions, the processing power required during input in such systems may tax the CPU or, in the case of the system of Barton, et al., require specialized hardware and software. Moreover, since much of what is recorded will not be played back in anything other than standard mode, the processing power required, and the memory required to store related index information, may be largely wasted. A more robust, cheaper, and less complicated system is needed.